Why do you think that lifeguards are working on the beach

Life guards keep watch over areas of water where there is activity, such as pools, oceans beaches, some lakes and rivers (that's not a guarantee). The reason a lifeguard would work at a beach is the same he would work at a pool: to make sure everyone is safe, and to help when help is needed. 

You save lives (or at least are trained to). When lifeguarding at beaches and open water, private communities or the government hold ownership of the land and tend to offer raises each year. For example, in Long Island, New York, the state and county operated beaches have a raise of one dollar for each season you return. Hope it helps